Heat developable photographic materials are well-known and heat developable photographic materials and processes for using such photographic materials are disclosed, for example, in "Shashin Kogaku no Kiso, Hi-Gin-En Shashin-Hen (The Elementary Course of Photographic Engineering, Section of Nonsilver Photography)", pp. 242 to 255, Corona Publishing Co. (1982), and U.S. Pat. No. 4,500,626, etc.
A method of imagewise forming or releasing diffusible dyes by heat development and transferring these diffusible dyes to an image-receiving material has been proposed. In this method, a negative dye image and a positive dye image can be obtained by changing the kind of the dye-donating compound and the kind of silver halide to be used. Further details are disclosed in U.S. Pat. Nos. 4,500,626, 4,483,914, 4,503,137, 4,559,290, JP-A-58-149046, JP-A-60-133449, JP-A-59-218443, JP-A-61-238056 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), EP 220746 A2, Kokai Giho No. 87-6199 and EP 210660 A2, etc.
Various methods have been proposed as to methods of obtaining positive color images by heat development. For example, a method in which a so-called dye releasing redox compound (hereinafter referred to as a DRR compound) is converted to a compound of an oxidized form having no dye-releasing capability, and the compound, in the presence of a reducing agent or a precursor thereof, is heat developed, the reducing agent is oxidized corresponding to the exposure amount of silver halide by heat development, and the compound is reduced by the remaining reducing agent not oxidized to release diffusible dyes is disclosed in U.S. Pat. No. 4,559,290. Further, a heat developable color photographic material using, as a compound which releases diffusible dyes by the same mechanism, a compound which releases diffusible dyes by the reductive cleavage of N--X bond (wherein X represents an oxygen atom, a nitrogen atom or a sulfur atom) is disclosed in EP 220746 A and Kokai Giho No. 87-6199 (No. 22, Vol. 12).
Conventionally used color photographic materials generally have blue, green and red spectral sensitization. For forming images on such color photographic materials using image information once converted to electric signals, a color CRT (cathode ray tube) is generally used as an exposure light source but CRT is inappropriate for obtaining a large size print.
A light emitting diode (LED) and a semiconductor laser (LD) have been developed as a write head capable of obtaining a large size print, but a photo-write head which efficiently emits blue light has not been developed yet.
Accordingly, for example, when LED is used, it is necessary to use a light source combining three LED's of near infrared (800 nm), red (670 nm) and yellow (570 nm) for exposing color photographic materials having three layers spectrally sensitized to infrared, red and yellow. A system of image recording according to such configuration is described in "Nikkei New Materials", pp. 47 to 57, Sep. 14, 1987, and has partly been put to practical use.
Further, a system of recording on a color photographic material having three light-sensitive layers each having spectral sensitization in wavelength of 880 nm, 820 nm and 760 nm using a light source combining three LD's showing emission of each of these wavelengths is disclosed in JP-A-61-137149.
In general, when yellow, magenta and cyan colors in a multilayer color photographic material are colored by exposure to light in three different spectral regions, it is an important technique in color reproduction to develop each color without color mixing. In particular, when LED or LD is used as an exposure light source, it is unavoidable to design three spectral sensitivities in a spectral region of narrow range (from red to infrared region), therefore, how to lessen the overlap of each spectral sensitivity is the key to the improvement of color isolation.
For ensuring color isolation, as is disclosed in U.S. Pat. No. 4,619,892, techniques of making the sensitivity in short wavelength side successively high or using a filter are known. However, if the sensitivity in short wavelength side is made successively high, fog increases and raw stock storability deteriorates with the lapse of time. In infrared sensitization, it has been difficult to achieve high sensitivity due to desensitization by the addition of dyes and the low efficiency of color sensitization.
For solving these problems, color photographic materials excellent in color isolation, showing high sensitivity and good raw stock storability due to the use of an infrared sensitizing dye of a J-band type of high spectral sensitivity are disclosed in JP-A-4-146431 and JP-A-5-45828.
The above heat developable color photographic materials are used in combination with an image-receiving material which mordants a diffusible dye. When an image obtained in this image-forming system is used as a color-proof in the printing field, the color reproduction level of the image obtained by synthesizing dye images of three colors of yellow, magenta and cyan is an important factor. That is, it is necessary that the image obtained in such an image-forming system should be able to cover the color reproduction level equal to or higher than the level of images obtained using standard printing ink. Further, the tint of a white ground part is required to coincide with the whiteness of standard paper for printing.